1. The Field of the Invention
The present invention relates to apparatus and methods of high-content screening using imaging systems. More specifically, the present invention relates to calibration of such imaging systems.
2. The Relevant Technology
High-content screening (“HCS”) is a cell-based screening method that yields detailed information about the temporal-spatial dynamics of cell constituents and processes, and plays an important role in the use of cell-based screening for identification and validation of drug candidates. The information provided by HCS alleviates bottlenecks in the drug discovery process by providing deep biological information. The assays associated with this method use either fixed or live cells, depending on the biological information desired.
In one method of performing an HCS scan, the cells of interest are loaded into an array of wells in a standard specimen plate (also known as a titer or microtiter plate) with 96 wells. The specimen plate is then positioned in a plate holder on a stage within an imaging system so that the specimen plate can move horizontally with the stage. The imaging system also includes a microscope. Motors are attached to the stage so that the stage and the specimen plate can be moved with respect to the microscopy in both directions orthogonal to the microscope. As a result, any of the individual wells can be positioned in alignment with the microscope so as to be able to be imaged through the microscope objective.
During a typical scan, the stage is moved by the motors until one of the wells is aligned with the objective and one or more of the cells within that well are imaged through the objective. The entire well can be imaged at the same time, or various fields within the well can be individually imaged. To image the different fields within the well, the stage is moved into different positions by the motors so that the objective is aligned with each field. When imaging is completed for the well, the stage is then moved by the motors until another one of the wells is aligned with the objective and, similar to the previous well, one or more of the cells within the newly aligned well are imaged through the objective. This movement and imaging of each individual well continues until all of the wells have been imaged through the objective. Computerized analysis is then performed on the obtained images to determine information about the cells. This type of scanning can be performed many times a day for different HCS scans using the same machine. It would be a benefit to be able to easily check the machine either during an HCS scan or between HCS scans to quickly determine if any of the system parameters are outside of predetermined limits and need to be calibrated.
Furthermore, often, a single HCS scan will require more than the 96 cell samples available on the standard specimen plate. In those cases, more than one specimen plate of cells is used to determine information about the cells. To accomplish this, each specimen plate must be separately scanned, either in separate imaging systems or one after the other in the same imaging system. When using multiple specimen plates, it is desirous to compare the different HCS scans performed within the same or different imaging systems.
For the results of these different scans to be comparable, local differences in the imaging systems and software associated with the optics, illumination, geometry of the plate, or other assay-specific parameters, must be minimized to ensure reproducibility and value of the information derived from performing HCS.
Currently, calibration of an imaging system consists of using a custom plate or placing various calibration samples within various wells of a standard 96-well specimen plate, placing the custom plate or specimen plate within the plate holder, and imaging the plate similar to when performing an HCS scan. This is tedious and time consuming and can lead to potential errors and discrepancies. For example, loading and unloading a custom or specimen plate within an imaging system takes a finite amount of time that adds up when performing many HCS scans and calibrations. Furthermore, because the calibration requires loading and unloading a new plate each time, automation of the calibration process is not available. Finally, the user of the imaging system must be extremely careful to load up the calibration plate in exactly the same way each time and on each imaging system to be able to obtain the same calibration results. Otherwise, various discrepancies can occur. Because of the difficulties noted above and others, most imaging systems are calibrated only rarely by the end user.
Accordingly, it would be an improvement in the art to provide an imaging system that solves some or all of the above problems and/or other limitations known in the art.